Annual
average temperatures at the Byrd research station in West Antarctica
had risen 2.4 degrees Celsius (4.3F) since the 1950s, one of the
fastest gains on the planet and three times the global average in a
changing climate, it said.

The
unexpectedly big increase adds to fears the ice sheet is vulnerable
to thawing. West Antarctica holds enough ice to raise world sea
levels by at least 3.3 metres (11 feet) if it ever all melted, a
process that would take centuries.

"The
western part of the ice sheet is experiencing nearly twice as much
warming as previously thought," Ohio State University said in a
statement of the study led by its geography professor David Bromwich.

The
warming "raises further concerns about the future contribution
of Antarctica to sea level rise," it said. Higher summer
temperatures raised risks of a surface melt of ice and snow even
though most of Antarctica is in a year-round deep freeze.

Low-lying
nations from Bangladesh to Tuvalu are especially vulnerable to sea
level rise, as are coastal cities from London to Buenos Aires. Sea
levels have risen by about 20 cms (8 inches) in the past century.

The
United Nations panel of climate experts projects that sea levels will
rise by between 18 and 59 cms (7-24 inches) this century, and by more
if a thaw of Greenland and Antarctica accelerates, due to global
warming caused by human activities.

GLACIERS

The
rise in temperatures in the remote region was comparable to that on
the Antarctic Peninsula to the north, which snakes up towards South
America, according to the U.S.-based experts writing in the journal
Nature Geoscience.

Parts
of the northern hemisphere have also warmed at similarly fast rates.

Several
ice shelves - thick ice floating on the ocean and linked to land -
have collapsed around the Antarctic Peninsula in recent years. Once
ice shelves break up, glaciers pent up behind them can slide faster
into the sea, raising water levels.

"The
stakes would be much higher if a similar event occurred to an ice
shelf restraining one of the enormous West Antarctic ice sheet
glaciers," said Andrew Monaghan, a co-author at the U.S.
National Center for Atmospheric Research.

The
Pine Island glacier off West Antarctica, for instance, brings as much
water to the ocean as the Rhine river in Europe.

The
scientists said there had been one instance of a widespread surface
melt of West Antarctica, in 2005. "A continued rise in summer
temperatures could lead to more frequent and extensive episodes of
surface melting," they wrote.

West
Antarctica now contributes about 0.3 mm a year to sea level rise,
less than Greenland's 0.7 mm, Ohio State University said. The bigger
East Antarctic ice sheet is less vulnerable to a thaw.

Helped
by computer simulations, the scientists reconstructed a record of
temperatures stretching back to 1958 at Byrd, where about a third of
the measurements were missing, sometimes because of power failures in
the long Antarctic winters.

PASADENA,
Calif. - An international team of experts supported by NASA and the
European Space Agency (ESA) has combined data from multiple
satellites and aircraft to produce the most comprehensive and
accurate assessment to date of ice sheet losses in Greenland and
Antarctica and their contributions to sea level rise.

In
a landmark study published Thursday in the journal Science, 47
researchers from 26 laboratories report the combined rate of melting
for the ice sheets covering Greenland and Antarctica has increased
during the last 20 years. Together, these ice sheets are losing more
than three times as much ice each year (equivalent to sea level rise
of 0.04 inches or 0.95 millimeters) as they were in the 1990s
(equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of
the loss is coming from Greenland, with the rest from
Antarctica.

This rate of ice sheet losses falls within
the range reported in 2007 by the Intergovernmental Panel on Climate
Change (IPCC). The spread of estimates in the 2007 IPCC report was so
broad, however, it was not clear whether Antarctica was growing or
shrinking. The new estimates, which are more than twice as accurate
because of the inclusion of more satellite data, confirm both
Antarctica and Greenland are losing ice. Combined, melting of these
ice sheets contributed 0.44 inches (11.1 millimeters) to global sea
levels since 1992. This accounts for one-fifth of all sea level rise
over the 20-year survey period. The remainder is caused by the
thermal expansion of the warming ocean, melting of mountain glaciers
and small Arctic ice caps, and groundwater mining.

The
study was produced by an international collaboration -- the Ice Sheet
Mass Balance Inter-comparison Exercise (IMBIE) -- that combined
observations from 10 satellite missions to develop the first
consistent measurement of polar ice sheet changes. The researchers
reconciled differences among dozens of earlier ice sheet studies by
carefully matching observation periods and survey areas. They also
combined measurements collected by different types of satellite
sensors, such as ESA's radar missions; NASA's Ice, Cloud and land
Elevation Satellite (ICESat); and the NASA/German Aerospace Center's
Gravity Recovery and Climate Experiment (GRACE).

"What
is unique about this effort is that it brought together the key
scientists and all of the different methods to estimate ice loss,"
said Tom Wagner, NASA's cryosphere program manager in Washington.
"It's a major challenge they undertook, involving cutting-edge,
difficult research to produce the most rigorous and detailed
estimates of ice loss from Greenland and Antarctica to date. The
results of this study will be invaluable in informing the IPCC as it
completes the writing of its Fifth Assessment Report over the next
year."

Professor Andrew Shepherd of the University
of Leeds in the United Kingdom coordinated the study, along with
research scientist Erik Ivins of NASA's Jet Propulsion Laboratory in
Pasadena, Calif. Shepherd said the venture's success is because of
the cooperation of the international scientific community and the
precision of various satellite sensors from multiple space
agencies.

"Without these efforts, we would not be
in a position to tell people with confidence how Earth's ice sheets
have changed, and to end the uncertainty that has existed for many
years," Shepherd said.

The study found variations
in the pace of ice sheet change in Antarctica and Greenland.

"Both
ice sheets appear to be losing more ice now than 20 years ago, but
the pace of ice loss from Greenland is extraordinary, with nearly a
five-fold increase since the mid-1990s," Ivins said. "In
contrast, the overall loss of ice in Antarctica has remained fairly
constant, with the data suggesting a 50-percent increase in Antarctic
ice loss during the last decade."